Softness does not imply tendancy to crack.  Just the opposite in some cases.
  It's not clear how you propose to reduce the hole diameter by
compression.  You need to keep the hole round and also preserve the proper
taper...
  It might be easier to remove metal from the bottom of the arm than from
the edge of the shaft.  Extra washer like things might be needed on top if
the nut doesn't push down far enough.
 Good luck, report back.   :-)

On Thu, Feb 27, 2014 at 2:16 PM, Neil N <musomuso@gmail.com> wrote:

> Hi all.
>
> The wiper arm metal is soft (pot metal?) so I assume it's prone to
> cracking, but if one compressed the portion of metal on wiper arm that
> contacts the wiper arm shaft, would this reduce the ID of the hole on
> arm and enable the arm to better re-knurl to the wiper arm shaft?
>
> After repairing my '81 Westy yesterday, finally pulled my head out of
> the engine bay to see that snow load had forced a wiper arm on the '88
> to drop. I measured the length from shoulder of wiper arm shaft (below
> splines) to end of splines and length of portion of wiper arm that
> slides over the shaft. I saw just over 1 mm difference. The shaft is
> shorter. This gave me cause to file a **very, very ** small amount of
> metal off the shoulder of shaft to see if that would help the arm seat
> further down. It seemed to help wiper re-knurl, but all that spawned
> the above question.
>
> Neil.
>
>
>
> --
> Neil n
>
> Blog: tubaneil.blogspot.ca
>
> '88 Westy http://tinyurl.com/c8rlw6p
>
> '81 VanaJetta 2.0 "Jaco"  http://tubaneil.googlepages.com/
>
> Vanagon VAG *Gas* inline-VR Engine Swap Group:
>
> http://tinyurl.com/d7gd5ej
>